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Crossing Thresholds

May 28, 2013
Spring 2013

On January 30, the New England Fishery Management Council voted to reduce the total allowable catch for a number of groundfish stocks by significant margins. Fishermen face cuts in Gulf of Maine (GOM) cod, Georges Bank (GB) cod, GOM haddock, Cape Cod/GOM yellowtail flounder, witch flounder, and plaice. Reductions range from 12% to 77%, unprecedented year-on-year reductions. 

Has the Gulf crossed a threshold?

It is increasingly difficult to explain the stunning changes occurring in the marine environment without examining fundamental shifts in its physical and ecological conditions. Are these ecological changes substantial enough to cross some invisible threshold such that the future of the region's marine ecosystem will look very different from its past? How do we know? What do we do about it?

How do we know?

Clearly there have been major changes in the ecosystem in recent years. While commercial and recreational harvest has reduced cod's ability to weather change, fishing pressure alone does not explain its steady decline. Maine's lobster industry witnessed an unusually early lobster shed that flooded the market at the beginning of last summer. The range of some species is also expanding. For example, fishermen found squid and black seabass further north than normal this past year.

But couldn't these changes just be natural fluctuations? After all, cod abundance has risen and fallen. Squid have appeared in the Gulf of Maine before. Indeed, observing only top predators in the ecosystem may be deceptive; minor changes at the bottom of the food chain get amplified higher up. 

That leads to examining the more fundamental building blocks of the ecosystem: its underlying physical characteristics- temperature, salinity, nutrients, currents- and essential biological building blocks- phytoplankton and zooplankton. As the article about scientist Jeff Runge's research reveals, the physical conditions in the Gulf of Maine are changing to such an extent that one of the most important links between plankton and fish, the zooplankton called Calanus finmarchicus, may disappear from the Gulf of Maine over the next 40 years.

Water temperature, whether on the surface or at depth, has risen in the Gulf over the past several decades. Sea surface temperatures in the northwest Atlantic were 1 to 3 degrees Celsius (2 to 5 degrees Fahrehnheit) above the 30-year average and even higher in the Gulf of Maine in 2012. 

What do we do about it?

Fisheries management in the United States is based almost entirely on the idea that each commercially harvested species has an ideal population size that allows it to sustain itself while producing enough excess biomass to allow some level of extraction. Much of the Magnuson-Stevens Act is based on this premise.

In a stable ecosystem, this is a sensible approach. In a dynamic ecosystem that is changing rapidly, it might make sense to adopt a management system that does not rely on rebuilding all fish populations to historical levels but recognizes natural fluctuations and changed conditions.

A first step in this direction is to reexamine the underlying assumptions of the reference points scientists use to compare existing fish stocks to their historical levels. The Massachusetts Fisheries Institute, a collaboration between the University of Massachusetts School of Marine Science and Technology and the Massachusetts Division of Marine Fisheries, has announced a series of three workshops to take place this winter and spring that will do just that.

Meanwhile, the University of California-Santa Barbara's Marine Science Institute has just announced a four-year project to study marine ecosystem thresholds or 'tipping points.' The study will strengthen our understanding of how seemingly gradual change in the marine ecosystem may result in enduring shifts that need to be reflected in management decisions.

At GMRI, our science team focuses on ecosystemic-level research that reveals the dynamic connectivity of the ocean: examining the impact of climate change on marine habitats, understanding the life history and stock structure of key species like herring and cod, working with industry to develop more selective fishing gear, and analyzing the impact of the changing ecosystem on the region's seafood markets. These research efforts, in conjunction with others, will inform the development of management approaches that reflect variability and system change in the Gulf of Maine.

Related Links:

Andy Pershing: Cod in the Gulf of Maine blog post

NOAA Fisheries Gulf of Maine Cod News